This invention relates in general to furnace-type apparata and in particular to modular furnaces which may be adapted for use with a conventional domestic heating system.
Before the widespread availability of modern hot air heating systems, which are designed to use such fuels as natural gas and oil, homes and other structures were typically heated by means of coal-burning or wood-burning furnaces. Since such devices required manual loading of the firebox combustion chamber with an appropriate fuel, the efficiency of the furnace was of particular importance such that the user received the maximum heat out of the particular amount of combustible material being burned. When there is an insufficient supply of oxygen to such a fire, or to a particular portion of the fire, that portion will not experience complete combustion and finely divided particles of the fuel will be exhausted as smoke and soot. This smoke and soot represents both fuel waste as well as heating inefficiency.
Another aspect to the factor of efficiency is to what degree the heat generated by the fuel being burned will be provided to the portions of the structure which require such heat. Heat which escapes up through the exhaust stack of the furnace also represent inefficiency and waste. These and related problems of inefficiency and waste have been the subject of a number of patents which have attempted to provide some improvement to the state of the art as of the time of their conception. The following listed patents provide some indication of the design ideas which have been conceived.
______________________________________ U.S. Pat. No. Patentee Issue Date ______________________________________ 345,991 Reynolds 7/20/86 503,817 Watson 8/22/93 2,083,745 Risdon 6/15/37 2,130,894 Muir 9/20/38 2,822,136 Dalin 2/04/58 3,934,554 Carlson 1/27/76 2,810,380 Critten 10/22/57 ______________________________________
Reynolds discloses a combined steam generator and radiator wherein the heat from the fire in the firebox is imparted to water in the generator which is disposed above the firebox. Heat from the water is conducted to the air passing through air-circulating tubes which are positioned throughout the generator.
Watson discloses an apparatus for producing and utilizing gas for heating purposes. The apparatus includes a combustion chamber, a grate bar and a plurality of ducts and air passageways formed such that a downdraft is employed to facilitate the combustion of the fuel.
Risdon discloses a furnace design which incorporates a downdraft feature for greater efficiency and a hot water coil disposed within the firebox. A bypass for combustion gases is provided such that the furnace may be used for just the heating of the hot water coil.
Muir discloses a method and means for automatic temperature regulation for a domestic hot water heating system utilizing warm air from a domestic heating furnace. The device incorporates a special heat-dissipating coil positioned in the path of the air flow through the furnace for limiting the upper temperature to which the water may be heated.
Dalin discloses a combined hot air furnace and domestic water heater wherein the total available heat is automatically apportioned between the heating of air and the heating of water based upon the demands of each. The device incorporates a patented heat exchanger construction in an effort to reduce the overall size of the device.
Carlson discloses a water and room-heating unit for extracting heat from combustible material. The heating unit includes a firebox chamber formed from a plurality of water chambers that are arranged in a "U" shape and are interconnected by a first network of pipes which also function as grates and a second network of heat-extracting pipes having radial fins projecting therefrom. The firebox includes an air combustion control and a flue for extracting heat from the combusted gases to heat the surrounding atmosphere.
Critten discloses a wood-burning hot air furnace wherein means are provided for controlled and long burning of each charge of fuel. Automatic controls are included for maintaining substantially uniform temperature in the area being heated. The firebox of the furnace is surrounded by an air jacket for circulating heating air around the sides of the firebox.
Although these various patents disclose devices which attempt to maximize some feature or capability of a furnace, the most optimal construction is one which achieves complete combustion of the fuel being used and transfers a maximum amount of the heat produced by the fuel being combusted to the circulating heating air. Systems which provide combustion air to the firebox in a conventional manner, such as the draft door of the Critten patent, are not suitable for complete combustion due to the entry location of the air relative to the fuel being combusted. Similarly, devices which direct combustion air across only the top of the fire do not supply the necessary oxygen to the interior of the fire. Although there may be devices which introduce air beneath the fire, the optimal arrangement is one which both introduces air uniformly beneath the entire area of the fire an also introduces a portion of the total air above the fire. The reason for this is that as the air passes up through the fire, the oxygen will be used for combustion and in the event unburned particles and combustible gases remain, these combustible materials will move to the top of the fire. By providing a further supply of oxygen at this location above the fire, these remaining combustible materials can be burned. In order to enhance the occurrence of this total and complete combustion, a device having a downdraft feature with a closed top firebox, will temporarily trap the particles and gases in the upper portion of the firebox thereby providing additional time for the combustion of this material. None of the listed patents disclose the combination of such features. Furthermore, none of the listed patents disclose heat exchange means as part of the firebox which provides the most direct and therefore the optimal method of conducting and convecting firebox heat to the surrounding heating air.
Another consideration of any furnace apparatus is the availability of fuel. Due to the fact that heating oil, natural gas, coal and electricity may be of questionable availability during the heating season due to shortages, labor strikes and the inability to deliver due to bad weather, a modular furnace device which is able to burn items such as wood, paper, and coal, and which may be easily adapted to a conventional domestic heating system, offers significant advantages as a backup system when fuel availability is a consideration as well as an alternative when fuel cost is an important consideration.